Method of oxidizing olefins



METHOD OF ()XIDlZlNG OLEFINS Maynard M. Baldwin, Columbus, Ohio, assignor, by

mesne assignments, to Olin Mathieson Chemical Corporation, a corporation of Virginia No Drawing. Original application April 24, 1948, Serial No. 23,131, now Patent No. 2,688,603, dated September 7, 1954. Divided and this application December 23, 1953, Serial No. 400,142

4 Claims. (Cl. 260-604) This invention relates to a novel method of catalyzing the oxidation of olefins.

It is an object of this invention to provide a novel method for catalyzing the oxidation of olefins.

Other objects and advantages of the present invention will become apparent to those skilled in the art from the detailed description thereof as set forth hereinafter.

It has been disclosed in copen-ding application, Serial No. 23,131, filed April 24, 1948, now Patent No. 2,688,603, issued September 7, 1954, that a. highly active nited States Patent catalyst capable of promoting both diflicult and desirable 2 remove the organic portion of the molecule.

The novel results obtained by the catalyst comprising the present invention are believed to be due to the size (volume) of the precursor molecule and also to the relative isolation of the metal atom within the precursor from other metal atoms. Organic metallic compounds which are suitable as precursors are those in which each metal atom is chemically combined with at least two organic groups each containing four or more nonmetallic atoms in a chain or cyclic structure. The metal which con stitutes a portion of the precursor must, of course, be capable of catalytic activity. Metals which are characterized by catalytic properties, are commonly classified as those metals which possess at least one differentiating electron in the second from the outermost shell, or penultimate shell. Such a classification is set forth, for example, in the patent to Huiiman, No. 2,437,533, issued March 9, 1948. The class of metals having their differentiating electrons in the penultimate shell includes scandium, titanium, vanadium, chromium, manganese, iron, cobalt, nickel, copper, zinc, yttrium, zirconium, columbium, molybdenum, masurium, ruthenium, rhodium, palladium, silver, cadmium, lanthanum, hafnium, tantalum, tungsten, rhenium, osmium, iridium, platinum, gold, mercury, actinium, thorium, and uranium.

Taking the metal copper as an example, compounds which may be used as suitable precursors include copper phthalocyanine, copper hydroxyquinoline, copper complex of bis-acetoacetonylethylenediamine, copper caproate, copper Z-ethylhexoate, copper stearate, copper salt of uric acid, copper benzoate, copper diphenate, copper quinolate, copper salts of amino sulfonic acid such as 4-aminotoluene-3-sulfonate and copper 2-amino-5-naphthol-7-sulfonate, copper amino acetate, copper amino benzoate, copper resinate, copper salts of acids such as adipic, azela-ic, aconitic and aurin tricarboxilic acid, and their complexes with ethylenediamine.

This list of compounds is not exhaustive, and similar or comparable compounds, including the other metals of the named class, may be employed. For example, suitable precursors may be obtained from the S-hydroxyquinoline complexes with scandium, titanium, vanadium,-

i chromium, manganese, iron, cobalt, nickel, copper, zinc,

yttrium, zirconium, c-olumbium, molybdenum, ruthenium, rhodium, lead, silver, cadmium, lanthanum, hafnium, tantalum, tungsten, gold, mercury, actinium, thorium, palladium, and uranium. The copper, cobalt, manganese, iron, cadmium, lead, and nickel salts, of the naphthenic acids may also be employed.

Further examples of suitable precursors are bisdimethyl gly-ox-ime cobalto chloride; lanthanum hexa-antipyrine iodide; dipyridy-l perrhenate; nitron complex with rhenium; benzidene complex of osmium; dibenzyl mercury; diphenyl mercury; phenyl mercury propionate; anthranilates of zinc, cobalt, nickel, cadmium, manganese, copper, lead, and mercury; the thorium and lead salts of picrolonic acid; nickel and lead dimethylglyoximes; copper, cadmium, zinc, uranium, lead, silver, manganese, nickel, cobalt, iron, chromium, and titanium salts of quinaldinic acid; salicylaldox-ine of copper and platinum; cupferone complex of iron, copper, zinc, thorium, tantalum, and vanadium; mercaptobenzthiazol complex of gold; dithizon complexes of copper, mercury, cobalt, zinc, nickel, cadmium, manganese, iron, lead, palladium, and platinum; in addition to complexes of almost all of these metals with naphthaquinonedioxime.

Most satisfactory results have'been obtained with precursors in which the metal is combined with the organic radicals both through primary and through secondary valence bonds. These complexes appear to impart greater isolation to the metal atom. Precursors satisfactory for the present invention may thus be broadly defined as organic compounds containing a metal which has its differentiating electron in the penultimate shell and which is chemically combined with at least two organic groups each containing four or more nonmetallic atoms in a chain or cyclic structure. Precursors are preferred, however, which, in addition to answering the above requirements, contain metal atoms which are combined with the organic radicals both by primary and secondary valence bonds.

The present invention is concerned with the support employed only to the extent of the effect of that support upon the catalytic action of the catalyst. Consequently, any of the more commonly used supports which are widely known in the field of catalysis may be employed, such as alumina, magnesia, silica, zirconia, titania, thoria, alumina gel, silica gel, kieselguhr, and various clays. The most satisfactory results have been obtained, however, with porous refractory supports. Pumice has proven to be particularly satisfactory.

The distribution of the precursor over the support or carrier may take many forms, as long as the ultimate aim of obtaining a very thin layer of uniformly distributed precursor over the support surface is satisfied. Preferably, the precursor is dissolved in some solvent to effect a molecular dispersion therein and then applied in a dilute solution to the surface of the support. Precursors which cannot be conveniently dissolved in a suitable solvent may be dispersed in a slurry and applied in this form to the support material.

After the precursor has been applied in a thin layer to the surface of the support, the precursor-coated support is heated to remove the organic portion of the precursor molecule. It is critical, however, that only a small amount of metal or metal compound (not materially greater than 2 grams of metal per cc. of supported catalyst) formed from the precursor remain on the support. The residue remaining after heating is believed to be the metal oxide or the pure metal itself, although it is impossible to determine exactly the chemical composition of the residue. It is known, however, that the organic portion of the precursor-molecule is decomposed and driven olf and that the residue contains the metal portion of the precursor molecule. The particular temperature and time required to decompose the precursor will vary in each instance with the particular precursor involved. Some precursors are kfiown'to'deco mpose at temperatures as low as 100 F., whereas other precursors do not show visible signs of decomposition until temperatures inexces-s of 600 F; are reached. .Catalysts produced in accordance with the manner abovedescribed have a wide variety of ,uses. For example, these catalysts are suitable for catalyzing the oxidation of compounds such as the olefins, aralkyls, aryls, alkyl, heterocyclics, and the dehydrogenation of alcohols. More specifically, these catalysts may be used for synthesizing the production of benzaldehyde from toluene, phenol from benzene, acrolein from propylene, and methacrolein from isobutylene.

In order tomore clearly set forth the present invention and to better enable those skilled in the art to practice the same, the following detailed description of the production of methacrolein from isobutylene is set forth. Pumice was crushed in a crushing roller and screened. The ,8-to-l-6 mesh material was used as the catalyst support. This support material was boiled in concentrated nitric acid for 30 minutes and then washed with water and dried prior to coating with a catalyst precursor.

The coating of the pumice was effected by adding thereto an aqueous 22.9% copper phthalocyanine slurry containing approximately 200 milliliters of water. The catalyst was dried and then placed in a reaction tube and air passed therethrough for a period of approximately 4 hours and at a temperature of 350 to 400 C. The calculated concentration of the catalyst was 1.53 grams per 100 milliliters of support, on the basis of a copper oxide formation, or 1.22 grams for 100 milliters on the basis of free copper.

Following the oxidation of the precursor, a gas mixture containing 9 parts of air and 1 part of isobutylene was passed through the catalyst for a period of 2 /2 hours at a temperature of approximately 325 C. Yields of 32% of methacrolein were obtained under these conditions. The flow rate of the gases through the catalyst bed was approximately 250 milliliters of total gas per hour per liter of catalyst.

Considerable variation in the above limitations may be made without adversely aifecting the course of the reaction. For example, the temperature may be varied from 270 to 475 0, although it is preferred to maintain the temperature at 325 to 400 C. The optimum for synthesizing acrolein from propylene is 325 C., whereas the optimum for the synthesis of methacrolein from isobutyl one is about 380 C. The rate of flow may vary broadly from 200 to 800 milliliters of total gas per hour per liter of catalyst, although it is preferred to maintain the rate of flow within a range of 250 to 550 milliliters total gas per hour per liter of catalyst. The ratio of the air to the olefin mayvary from as much as 3:1 to 12:1, although a ratio of 9:1 is preferred because this appears to be approximately the stoichiometric amount of oxygen required for the synthesis. The above limitations apply also to the production of acrolein from propylene.

The criticalness of the size of the molecule of the precursor may be brought out by comparing the results obtained in the above example using copper phthalocyanine with results obtained when copper nitrate isemployed. A copper nitrate precursor was dissolved and distributed upon a pumice support in a manner identical with thatdescribed above in connection with the copper phthalocyanine. After the copper nitrate was decomposed by heat, the catalyst was employed to oxidize isobutylene to methacrolein. The highest yields obtainable with this catalyst were only around 14% when the free copper in thecatalyst equalled or approximated the free copper in the copper phthalocyaninel It is believed that some explanation of the theory in back of the operation of this catalyst is important in carrying out the actual practice of the present invention. Qnce this theory is understood, wide application of this invention will become immediately apparent to those skilled in the art. Catalysis is admittedly largely a surface phenomenon. The most generally accepted theory of catalysis is that there exists a multitude of active centers on each catalyst which are sources of activation energy for the chemical reactants that are adsorbed and desorbed at these points to effect the desired reactions. It is believed that these active centers consist of a somewhat different crystal formation from the surrounding material and therefore have the peculiar characteristic of absorption and desorption so vital in catalysis. The activity of a catalyst is determined by the number of active centers per weight or per volume of catalyst.

In the present invention, the metal in the precursor is surrounded by organic radicals. The precursor is then spread thinly over a support surface and decomposed, leaving relatively isolated deposits of metal or metal oxides upon the surface of the support. Because of the extremely high state of division of the metal in the precursor, sometimes approaching molecular division, a much greater surface area per weight of metal is obtained. Consequently, there is a greater surface upon which active centers may occur. Also, because of the relative isolation of the metal molecule, there is a greater probability of their being in the active state.

This theory is borne out by actual observations. As above stated, catalysts used in the present invention are more active than catalysts of the prior art. Furthermore, high temperatures have little efiect on these catalysts. This can be explained by the fact that, because of their relative isolation, there cannot be melting together of adjacent metal deposits so as to destroy active centers by sintering. In addition, the isolation of the metal deposits is shown by the fact that the small molecules, such as copper nitrate, which do not afford opportunity for isolation of the metal, do not have the increased activity of these larger molecules. Furthermore, it has been found that higher concentrations of the precursor on the surface of the support decrease the activity of the catalyst rather than increase it. In terms of the above-set-forth theory, this means that too high concentrations of the precursor cause overlapping deposits of metal residue and thus decrease the probability of formation of the active centers which otherwise would increase the catalytic action.

It is apparent from the above description that the present invention relates to a novel method for oxidizing olefins wherein the olefin in the presence of oxygen is passed over a catalyst composed of a support and a residue formed in situ upon a support by decomposition thereon of a layer of an organic compound which contains a metal having its differentiating electron in the penultimate shell, and which is attached to at least two organic groups each having four or more nonmetallic atoms in a chain or cyclic structure. Included within the scope of this invention are precursors in which the above organic groups may be interconnected otherwise than at the metal. The extremely good yield obtained with these catalysts makes possible commercialization of processes heretofore thought impossible.

This is a division of copending application Serial No. 23,131, filed April 24, 1948, now Patent No. 2,688,603, issued September 7, 1954.

What is claimed is:

1. The method of oxidizing olefins which comprises passing the olefin, in the presence of oxygen, over a catalyst composed of a support and a residue formed in situ upon the support by distributing over the surface thereof copper phthalocyanine, and heating the thus coated support until the corresponding oxide of copper is formed.

2. A method of obtaining methacrolein from isobutylene which comprises passing a mixture of air and isobutylene over a catalyst composed of a support and a residue formed in situ on the support by distributing over the surface thereof copper phthalocyanine, and heating the thus coated support until the corresponding oxide of copper is formed.

3. A method of synthesizing methacrolein which comprises passing a mixture of air and isobutylene in ratios ranging from 3:1 to 12:1, at temperatures ranging from 270 to 475 C., and at flow rates ranging from 200 to 800 milliliters of total gas per hour per liter of catalyst, over the catalyst defined in claim 2.

4. A method of obtaining methacrolein from isobutylene which comprises passing a mixture of 9 parts of air 10 to one part of isobutylene over a catalyst as defined in claim 2, at a temperature of about 375 C. and at a flow rate of about 250 milliliters of total gas per hour per liter of catalyst.

References Cited in the file of this patent UNITED STATES PATENTS 2,627,527 Connolly et a1 Feb. 3, 1953 

1. THE METHOD OF OXIDIZING OLEFINS WHICH COMPRISES PASSING THE OLEFIN, IN THE PRESENCE OF OXYGEN, VOER A CATALYST COMPOSED OF A SDUPPORT AND A RESIDUE FORMED IN SITU UPON THE SUPPORT BY DISTRIBUTING OVER THE SURFACE THEREOF COPPER PHTHALOCYAMINE, AND HEATING THE THUS COATED SUPPORT UNTIL THE CORRESPONDING OXIDE OF COPPER IS FORMED. 